Tar-Palantir becomes King of Númenor
Event Type: Political
Age: Akallabêth/Last Alliance
He assumed the sceptre on the death of his father, Ar-Gimilzôr:
He was born in the year 3035, and he ruled for 78 years until his death in 3255.
Unfinished Tales, Part 2, Ch 3, The Line of Elros, Kings of Númenor
But when Inziladûn acceded to the sceptre, he took again a title in the Elven-tongue as of old, calling himself Tar-Palantir, for he was far-sighted both in eye and in mind, and even those that hated him feared his words as those of a true-seer. He gave peace for a while to the Faithful; and he went once more at due seasons to the Hallow of Eru upon the Meneltarma, which Ar-Gimilzôr had forsaken. The White Tree he tended again with honour; and he prophesied, saying that when the Tree perished, then also would the line of the Kings come to its end. But his repentance was too late to appease the anger of the Valar with the insolence of his fathers, of which the greater part of his people did not repent. And Gimilkhâd was strong and ungentle, and he took the leadership of those that had been called the King's Men and opposed the will of his brother as openly as he dared, and yet more in secret. Thus the days of Tar-Palantir became darkened with grief; and he would spend much of his time in the west, and there ascended often the ancient tower of King Minastir upon the hill of Oromet nigh to Andúnië, whence he gazed westward in yearning, hoping to see, maybe, some sail upon the sea. But no ship came ever again from the West to Númenor, and Avallónë was veiled in cloud.
The Silmarillion, Akallabêth
A final discrepancy between "The Line of Elros" and the Tale of Years arises in the dates of Tar-Palantir. It is said in the Akallabêth... that "when Inziladûn acceded to the sceptre, he took again a title in the Elven-tongue as of old, calling himself Tar-Palantir"; and in the Tale of Years occurs the entry: "3175 Repentance of Tar-Palantir. Civil war in Númenor." It would seem almost certain from these statements that 3175 was the year of his accession; and this is borne out by the fact that in "The Line of Elros" the death-date of his father Ar-Gimilzôr was originally given as 3175, and only later emended to 3177.
Unfinished Tales, Part 2, Ch 3, The Line of Elros, Kings of Númenor: Notes, Note 15
I have listed the two separate dates, but clearly Christopher Tolkien considers them as the same event.
added quote: Elena Tiriel 3Nov05